1. Technical Field
The present invention relates to the construction of engine crankshafts and, more particularly, to the art of making internal oil passages within such crankshafts.
2. Description of the Prior Art
It is known to incorporate oil ducts in an engine crankshaft to enable lubrication of the main bearings and the big end bearings. Such a construction is advantageous as it allows oil to be fed from a single point to all the bearings of the crankshaft instead of oil being pumped to each main bearing individually.
As is commercially practiced, a duct is formed by drilling axially aligned bores in the crankshaft and plugging the ends of the bores. Radial bores are also machined to further carry the oil to necessary locations. The drilling of the bores in this case is time consuming, not highly cost effective, and accuracy is required to ensure that the bores are correctly aligned to form a continuous duct. Furthermore, there is a tendency for air bubbles to be trapped at discontinuities in the ducts or at their juncture giving rise to inadequate lubrication.
In a further prior art proposal, plastic oil pipes are placed within a hollow crankshaft and a foamed plastic material is cast in the crankshaft to hold the oil pipes in place. In this case, the hollow crankshaft is weakened, especially at the webs of the cranks.